I'll ignore the post above me and just give my opinion; Jiggs isn't going anywhere, like it or not. If anyone's gonna be cut for Mewtwo, it's gonna be Pokemon Trainer, as he takes up half of the Pokemon roster slots already, and isn't in the original 12. Lucario might be cut as well, but it would be in place of a new Pokemon, if at all. Also, the original 12 is not laziness, it's tradition, as Pieman said. Those are the characters that three generations of Smashers have seen in the games, and who will always be there to use. There would be backlash for axing PT, of course, but there would be just as much backlash for axing Jiggs, no matter how much you hate her. I know lots of people who main her.
Great argument and all about Jigglypuff, I totally agree. No matter how much she is hated, she won't leave simply for nostalgic worth, and while she has a few haters, she has many supporters as well.
But I don't think you understand what "slot" means. Pokemon Trainer takes up ONE pokemon slot, but he is consisted of three characters. Just like Samus and Zero Suit Samus are different characters, but take up one slot. The same goes for Zelda and Shiek.
Since when did smash have "slots" and how do we know that lucario and pktrainer replaced mewtwo? im sure if sakuri said "we didnt have room for mewtwo because we put in meta knight" people wouldn't care nearly as much...the point being people are looking for an excuse to get rid of characters they dont like
Slots is a common term used to refer to a section of the roster that a character takes up. Pokemon Trainer, while being three characters, takes up one slot. We have 39 characters in Brawl but we only have 35 slots. Make sense now? If you don't like it then I'd suggest you leave, you're going to here the term quite a lot around here.
And while Mewtwo was cut mainly due to time, you could say that he was replaced by the Pokemon Trainer and that Pichu was replaced by Lucario (Pokemon Trainer/Mewtwo = first generation characters, Pichu/Lucario = new-generation representatives). It is obvious that Sakurai decided to cap the slots at four (as seen by Mario, Zelda, and Pokemon). It would be wierd for Pokemon to have five and Zelda or Mario to have four, right? So maybe there was more time to finish Mewtwo, but Dr. Mario and Toon Zelda (the late scraps for Mario and Zelda) probably couldn't be finished in time, Mewtwo wasn't finished either, because it would: 1.) Give Pokemon to much representation, including 1st-gen representation; .2) Give Pokemon more slots than Mario and Zelda which would be really unecessary.
Ahh, my mistake. I thought Peach and Pit were official.
I'd say Dry Bowser, but I doubt he actually would be unique, and be more or less a Bowser clone.
Waluigi WOULD be nice as a playable character, as would some other villains such as Petey Pirahna and if they decide more Sonic characters, Dr. Robotnik (Is there even a difference between Dr. Eggman and Dr. Robotnik?)
As for other possible characters, I personally liked the Pokemon Trainer concept, and think that it could be implemented again, maybe instead of Generation One Pokemon, they copuld have Generation Two Pokemon, such as Chickorita, Quilava and Feraligatr (I'd prefer Totodile, Bayleef and Typhlosion, but I'm pretty sure that the other three are preferred more).
Also, perhaps instead of Jigglypuff, we bring back Mewtwo, or maybe bring in Darkrai. Not sure how Darkrai would work though.
Another character I'd like to see is Paper Mario. His games would surely give him some unique moves. Such as the badges you could wear, and the Pixels. Items such as the Super Hammer, and the Super Boots would be good items as well.
Honestly, don't expect Dry Bowser or Waluigi. Petey Piranha will never happen either, he is more fit for a boss and he really isn't very significant to the Mario series. There are plenty more deserving Mario characters like Bowser Jr., Toad, and like you mentioned, Paper Mario.
There is an EXTREMELY low chance that we will see multiple representation from a single Third Party series, which means no new Sonic characters. While we have seen the introduction of Third Party series, this is still a Nintendo game, and more characters actually significant to Nintendo itself deserve these slots, not more guest characters.
I'm pretty sure the Pokemon Trainer's Pokemon will remain the same, but I agree that it is possible that we could see a different generation represented, probably the second (for the revival of Gold/Silver) like you said. And as much as people want Mewtwo to return, it isn't very likely at all, unless we see a VERY unnecessary amount of representation for Pokemon. Jigglypuff will stay for the reasons I stated above. While she has haters, she also has many fans, and she will stay for nostalgic worth and the such, things that Sakurai actually cares about as stated by Starpheonix earlier.